In some thermal power plants that generate high pressure, high temperature gas or steam that is passed through a turbine to generate power, the flow of hot gases to the turbine cannot be instantaneously reduced or prevented by simply controlling the gas generator. In a steam turbine power plant for example, the steam generator (boiler) cannot be shut down and re-started instantaneously. In the event of shutdown of the turbine in a thermal power plant, for example during load rejection, a turbine bypass system is, therefore, needed to prevent the admission of hot gases (such as steam) into the turbine.
Known turbine bypass systems include a gas cooler which cools the bypass gases. The components of the gas cooler are subjected to severe thermal stresses during initial operation of the bypass system due to the large temperature difference between the hot bypass gases and the relatively cool components of the gas cooler. Mechanical failure of the components is, therefore, common.
Attempts have been made to reduce the temperature of the bypass gases before delivery to the gas cooler, but component failure has still been encountered. There is, therefore, a need for an improved turbine bypass system.